1. Field of the Invention
This invention pertains to apparatus and methods for producing finished masonry building materials from masonry units of either the concrete or fired varieties. More particularly, the present invention relates to an apparatus and method for subjecting such masonry units to abrasion treatment in order to produce therefrom finished masonry building materials of a predetermined size and surface finish quality.
2. Background Art
It is common in building construction to employ both fired and concrete masonry units. The latter are comprised of an aggregate, such as cinders, gravel, or sand held together by a binder, such as cement. The cinders often used in such concrete masonry units can be either man-made or volcanic in origin. The use of cinders as aggregate initially led to such blocks being referred to as "cinder blocks." The manufacture of concrete masonry units typically involves the pressurized extrusion of a slightly moist mix of aggregate and binder from a mold, followed by curing.
Initially, concrete masonry units were coarse in appearance and bore drab colors that have become associated with industrial settings. Thus, while concrete masonry units were also employed in residential and commercial locations, their appearance dictated that they be used only in unexposed walls.
Such construction materials when artfully fabricated, however, offer greater potential as attractive constituents of exposed walls. Colors can be added to the cement binder of the aggregate to produce concrete masonry units in a variety of hues. For example, iron oxide is utilized in this role to produce a concrete masonry block giving the appearance of red sandstone. In addition, it is possible to vary the color, size and density of the aggregate particles that are sustained by the binder. By using these devices some degree of variety can be introduced into the appearance of concrete masonry units, but without further treatment such masonry units will still be afflicted with a dull, rough surface appearance which may make them yet readily identifiable as only brighter versions of the old "cinder block."
In an effort to overcome this lingering association, and in order to produce finished masonry building materials of a consistent and precise size, concrete masonry units are subjected following curing to abrasion treatment in the form of grinding and cutting. This more attractively exposes the aggregate and the cement binder thereabout. Through the process of cutting and grinding, finished masonry building materials can be produced having a uniform, predetermined size and a variety of surface finish qualities. These finished masonry building materials are termed variously ground face, honed, or burnished masonry blocks.
Optionally, cement pastes or sealers can be applied to fill the pores in the surface and to preserve the freshness of the aggregate color and the binder patterns revealed by abrasion treatment. Heavier sealers produce a glossy surface on such finished masonry building materials. Occasionally cement paste is applied even prior to abrasion treatment.
It has also been found appropriate to use such cutting and grinding techniques in sizing and surface finishing of fired masonry blocks, such as bricks and paving stones. Accordingly, throughout the balance of this disclosure and the claims appended thereto, the term "masonry unit" will be used to mean an uncut, unpolished, unground concrete or fired masonry unit. Correspondingly, the product produced by cutting, grinding, or polishing masonry units as defined above will be referred to hereinafter as "finished masonry building materials". Thus, finished masonry building materials as used herein includes ground face, burnished, or honed concrete or fired masonry units in finished form.
For these reasons there is an upsurge of interest in the use of concrete masonry units in exposed walls in residential, retail, educational, governmental, and religious structures. Through the use of the techniques already mentioned, such humble building materials can be provided with a distinctive appearance or one elegant enough to be taken for terrazzo or cut stone. The edges of concrete masonry units can be ground into various shapes and the surfaces may be provided with attractive architectural relief. Naturally, the cost per square foot of producing such materials is quite competitive with the cost of quarrying, cutting, polishing, and setting natural stone itself. In fact, all that has been said above about improving the surface appearance of concrete masonry units also applies to those fired masonry units which may lack aggregates and are cured by baking in high temperature ovens. Therefore, a need has been perceived in the construction industry to develop sophisticated methods and apparatus using abrasion treatment to produce from inexpensive masonry units finished masonry building materials acceptable for an installation, even in the exposed portions of non-industrial structures.
The accident that masonry units when once cut and polished tend to resemble more expensive cut and polished natural stone has hampered the efforts to develop production equipment and methods specifically suited to the new man-made building materials. Instead, and inappropriately, the grinding and sawing techniques and equipment formerly utilized in natural stone quarrying and processing have been adopted wholesale in the finishing of masonry units. Techniques applicable to marble and terrazzo have been imported without careful consideration of their costliness or complexity into machinery designed to cut and polish fired masonry units and aggregates of cinder, gravel, and sand. The resulting devices were unduly heavy, extremely complex, and naturally expensive to acquire and maintain. This, in turn, added needlessly to the cost of the otherwise economical building materials produced from masonry blocks.
For example, due to the relatively high cost of producing from original stone even a single precision cut and polished piece, the equipment by which to finish natural stone did not employ continuous production line concepts that might have been appropriate with a less expensive product. Most cutting and polishing devices for natural stone treated the work pieces one at a time, using complex positioning and position sustaining equipment. When this approach was transferred directly into processing equipment for inexpensive masonry units, production output levels resulted that were substantially less than which should have been produced with relatively inexpensive products. Mass market economical construction materials were unfortunately being fabricated using approaches appropriate to individually crafted, artisan products.
By and large, because of historical roots which extended by accident into the natural stone processing industry, early equipment for the cutting and grinding of masonry units exhibited a tendency to over-kill. Massive equipment utilizing overly powerful drive mechanisms were more than adequate to the task at hand, but once in place as capital equipment these tended to needlessly drive up the cost of the finished masonry building materials being produced.
In other ways the components of such masonry block processing equipment exhibited an ironic inappropriateness. Natural stone being relatively hard and fine grained, was attacked in abrasive treatments by fine grained and fine toothed saws, sanding belts, and disk-shaped polishing pads at low speeds. When such components, ideally suited to processing natural stone, were unthinkingly incorporated into an environment for processing relatively soft and extremely coarse masonry building materials, the over-kill capacity elsewhere apparent in the processing equipment, resulted in dysfunction. Working heads appropriate to processing natural stone turned out to have quite short lifetimes when pitted against the softer, unpredictable compositions of concrete masonry units. Thus, working head failure was frequent, resulting in high maintenance costs and expensive downtime losses.
As the industry wrestled with the technology it had inherited, there became apparent a need to stand back and examine the process as a whole in order to arrive at a contemporary overall design that met the needs of the industry involved. Such an approach is embodied in the invention disclosed hereafter.